Passion not many displayed for European plant (8)
I believe the answer is:
feverfew
'plant' is the definition.
(feverfew is a kind of plant)
'passion not many' is the wordplay.
'passion' becomes 'fever' (I can't explain this - if you can you should give a lot more credence to this answer).
'not many' becomes 'few' ('few' is the opposite to 'many').
'fever'+'few'='FEVERFEW'
'displayed for european' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Another definition for feverfew that I've seen is " Medicinal plant".)